Stacks of optical fiber ribbons closely bound by respective buffer encasements with relatively hard exteriors and relatively soft interiors, associated methods, and associated fiber optic cables

ABSTRACT

A stack of optical fiber ribbons is enclosed in a buffer encasement having a relatively soft inner portion and an relatively hard outer portion. The inner portion has an interior surface extends around and defines a longitudinally extending passage that contains the stack, and the interior surface closely bounds the stack. The outer portion extends around, closely bounds and contacts the inner portion, and has a modulus of elasticity that is greater than the modulus of elasticity of the inner portion. In accordance with one example of the invention, the inner portion has an exterior surface that extends around and is spaced apart from the passage, and the outer portion has an interior surface that extends around, closely bounds, and engages the exterior surface of the inner portion, whereby the buffer encasement has multiple plies. In contrast, in accordance with another example of the invention, a surface is not defined between the inner portion and the outer portion.

FIELD OF THE INVENTION

The present invention pertains to fiber optic cables and, moreparticularly, to protecting stacks of optical fiber ribbons withinbuffer encasements.

BACKGROUND OF THE INVENTION

Optical fiber is a very popular medium for large bandwidth applications,and as a result there is a demand for fiber optic cables with greaternumbers of optical fibers. In response to demands for increased opticalfiber count in fiber optic cables, optical fiber ribbons have beendeveloped. Optical fiber ribbons are planar arrays of optical fibersthat are bonded together as a unit. Optical fiber ribbons areadvantageous because many ribbons can be stacked on top of each other toform a stack of optical fiber ribbons.

It is conventional for stacks of optical fiber ribbons to beincorporated into two different types of fiber optic cables that aregenerally referred to as “central-core” and “loose-tube” cables. In thecentral-core design, a stack of optical fiber ribbons is containedwithin a central tube that is located at the center of the fiber opticcable. Strength members are positioned between the central tube and anouter plastic jacket of the cable. In contrast, loose-tube fiber opticcables typically include a number of relatively small buffer tubes thatare positioned around a central strength member, and each buffer tubeencloses a stack of optical fiber ribbons. The buffer tubes arelongitudinally stranded around the central strength member, meaning thatthe buffer tubes are rotated around the central strength member alongthe length of the fiber optic cable.

It is conventional for the above-referenced tubes to provide at leastsome protection for the optical fibers therein. It is important foroptical fibers to be protected from stain because strain can degrade theperformance of the optical fibers. For example, it is conventional forthe above-referenced tubes to be round, and for the stacks of opticalfiber ribbons to be generally rectangular. Therefore, for each tube andthe stack of optical fiber ribbons it contains, there is space definedbetween the interior surface of the tube and the periphery of the stack.In some applications that space is utilized to allow for relativemovement between the stack of optical fiber ribbons and the tube, andthat relative movement diminishes the stresses to which the opticalfibers are exposed. However, in some applications that space can becharacterized as wasted space. In some applications that space is filledwith a gel, such as a thixotropic gel, that cushions the stack ofoptical fiber ribbons to diminish the stresses to which the opticalfibers are exposed. However, in some applications those gels areconsidered a nuisance because they are messy and must be dealt with whenentering a fiber optic cable for the purpose or inspection, for forminga splice between optical fibers, or the like. In addition, for agenerally rectangular stack of optical fiber ribbons within a roundtube, the optical fibers at the corners of the stack will often bear thebrunt of any stresses.

Whereas there are several different conventional approaches forprotecting stacks of optical fiber ribbons from stress by enclosing thestacks in tubes, further improvements in this area would be beneficial.

SUMMARY OF THE INVENTION

The present invention provides for the cushioned packaging of a stack ofoptical fiber ribbons by enclosing the stack in a buffer encasementhaving a relatively soft inner portion and an relatively hard outerportion. More specifically, the inner portion has an interior surfaceextends around and defines a longitudinally extending passage thatcontains the stack, and the interior surface closely bounds the stack.More specifically, the interior surface of the inner portion engages asubstantial portion of the periphery of the stack. The outer portionextends around, closely bounds and contacts the inner portion, and has amodulus of elasticity that is greater than the modulus of elasticity ofthe inner portion.

In accordance with one aspect of the present invention, the innerportion has an exterior surface that extends around and is spaced apartfrom the passage, and the outer portion has an interior surface thatextends around, closely bounds, and engages the exterior surface of theinner portion, whereby the buffer encasement has multiple plies. Incontrast, in accordance with another aspect of the present invention, asurface is not defined between the inner portion and the outer portion.

In accordance with another aspect of the present invention, the bufferencasement is relatively thin. More specifically, each optical fiberribbon includes a pair of longitudinally extending opposite edges and apair of longitudinally extending opposite surfaces that extend laterallybetween the edges, and each optical fiber ribbon has a thickness definedbetween its opposite surfaces. In an end elevation view of the bufferencasement at least a majority of the buffer encasement has a thicknessdefined between the interior surface of the inner portion of the bufferencasement and an exterior surface of the outer portion of the bufferencasement, and the thickness of the buffer encasement is notsubstantially greater than the thickness of each of the optical fiberribbons.

In accordance with another aspect of the present invention, the bufferencasement is sufficiently rigid to maintain the stack in a stackedconfiguration and sufficiently flexible to allow the optical fiberribbons to slide laterally relative to one another so that, in an endelevation view of the stack, the stack and the buffer encasement cantransition from a non-skewed configuration to a skewed configuration.The lateral displacement between the optical fiber ribbons in the skewedconfiguration is different from the lateral displacement between theoptical fiber ribbons in the non-skewed configuration.

In accordance with another aspect of the present invention, the stack islongitudinally twisted, the buffer encasement is sufficiently rigid tohold the stack in the longitudinally twisted configuration, and thebuffer encasement is thin such that an exterior surface of the outerportion of the buffer encasement defines ridges that correspond to thetwist of the stack.

In accordance with another aspect of the present invention, the interiorsurface of the buffer encasement is unadhered to the stack and the stackis capable of moving relative to the buffer encasement.

In accordance with another aspect of the present invention, theperiphery of the stack defines a shape in an end elevation view of thestack, and the interior surface of the inner portion of the bufferencasement defines a shape in an end elevation view of the bufferencasement that is substantially similar to the shape defined by theperiphery of the stack in the end elevation view of the stack.

In accordance with another aspect of the present invention, in the endelevation view of the buffer encasement, the exterior surface of theouter portion of the buffer encasement defines a shape that issubstantially similar to the shape defined by the periphery of the stackin the end elevation view of the stack.

In accordance with another aspect of the present invention, the bufferencasement is formed by coating the stack with an ultraviolet-curablematerial and thereafter exposing the ultraviolet-curable material toultraviolet radiation for a predetermined period of time selected sothat on a per unit basis more curing occurs in the outer portion thanthe inner portion.

In accordance with another aspect of the present invention, the bufferencasement is formed by extruding a first extrusion around the stack andextruding a second extrusion around the first extrusion so that theinterior surface of the second extrusion comes into contact with theexterior surface of the first extrusion prior to solidification so thatthe interior and exterior surfaces become blended together.

In accordance with another aspect of the present invention, the bufferencasement is formed by applying a film around the stack and extrudingan extrusion around the film. Alternatively, the film may be appliedover the extrusion, or the extrusion may be replaced with a film. In allcases, the film may be either longitudinally folded or helically wrappedaround the stack, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an optical module in accordance with afirst embodiment of the present invention.

FIG. 2 is an end elevation view of the optical module of FIG. 1.

FIG. 3 is an isolated perspective view of an optical fiber ribbon of theoptical module of FIG. 1.

FIG. 4 is an isolated end elevation view of a stack of optical fiberribbons of the optical module of FIG. 1.

FIG. 5 is an end elevation view of the optical module of FIG. 1 in askewed configuration, in accordance with the first embodiment of thepresent invention.

FIG. 6 is partially schematic, isolated end elevation view of a bufferencasement of the optical module of FIG. 1.

FIG. 7 is a perspective view of an optical module in accordance with asecond embodiment of th present invention.

FIG. 8 is a partially schematic, end elevation view of an optical modulein accordance with a third embodiment of the present invention.

FIG. 9 is a partially schematic, end elevation view of an optical modulein accordance with a fourth embodiment of the present invention.

FIG. 10 is a perspective view of an optical module in accordance with afifth embodiment of the present invention.

FIG. 11 is an end elevation view of the optical module of FIG. 10.

FIG. 12 is a perspective view of an optical module in accordance with asixth embodiment of the present invention.

FIG. 13 is an end elevation view of the optical module FIG. 12.

FIG. 14 is an end elevation view of an optical module in accordance witha seventh embodiment of the present invention.

FIG. 15 diagrammatically illustrates an assembly of manufacturingequipment that is operative for manufacturing optical modules, inaccordance with several methods of the present invention.

FIG. 16 is a schematic end elevation view of a fiber optic cable inaccordance with an eighth embodiment of the present invention.

FIG. 17 is a schematic end elevation view of a fiber optic cable inaccordance with a ninth embodiment of the present invention.

FIG. 18 is a schematic end elevation view of a fiber optic cable inaccordance with a tenth embodiment of the present invention.

FIG. 19 is a schematic end elevation view of a fiber optic cable inaccordance with an eleventh embodiment of the present invention.

FIG. 20 is a schematic an end elevation view of a fiber optic cable inaccordance with a twelfth embodiment of the present invention.

FIG. 21 is a schematic end elevation view of a fiber optic cable inaccordance with a thirteenth embodiment of the present invention.

FIG. 22 is an isolated perspective view of a central member of a fiberoptic cable in accordance with a first version of the thirteenthembodiment of the present invention.

FIG. 23 is an isolated perspective view of a central member of a fiberoptic cable in accordance with a second version of the thirteenthembodiment of the present invention.

FIG. 24 is a schematic end elevation view of a fiber optic cable inaccordance with a fourteenth embodiment of the present invention.

FIG. 25 is a schematic end elevation view of a fiber optic cable inaccordance with a fifteenth embodiment of the present invention.

FIG. 26 is a schematic end elevation view of a fiber optic cable inaccordance with a sixteenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

FIGS. 1-14 illustrate optical modules 30 a, 30 b, 30 c, 30 d, 30 e, 30f, 30 g in accordance with preferred embodiments of the presentinvention. Methods of manufacturing the optical modules 30 a, 30 b, 30c, 30 d, 30 e, 30 f, 30 g are described with reference to FIG. 15, whichdiagrammatically illustrates an assembly of manufacturing equipment.Each of the optical modules 30 a, 30 b, 30 c, 30 d, 30 e, 30 f, 30 g inisolation can be characterized as a fiber optic cable, or each of theoptical modules can be a component of a fiber optic cable that includesother components, such as an outer jacket that surrounds one or moreoptical modules. FIGS. 16-26 illustrate such fiber optic cables andcomponents thereof. Accordingly, this Detailed Description of theInvention section includes an Optical Modules subsection, a Methods ofManufacturing Optical Modules subsection, and a Fiber Optic Cablessubsection.

OPTICAL MODULES

First Embodiment

FIGS. 1 and 2 are perspective and end elevation views, respectively, ofan optical module 30 a in accordance with a first embodiment of thepresent invention. The optical module 30 a extends in a longitudinaldirection and is uniform along its length. The optical module 30 aincludes a longitudinally extending ribbon stack 32 a. The ribbon stack32 a is uniform along its length and is a stack of longitudinallyextending optical fiber ribbons 34. The optical module 30 a furtherincludes a longitudinally extending buffer encasement 36 a, which ispreferably in the form of a thin sheath, that is uniform along itslength and extends around and closely encases the ribbon stack 32 a. Thebuffer encasement 36 a can also be referred to or characterized as anenclosure. The buffer encasement 36 a is preferably constructed of apolymeric material. Specifically, the buffer encasement 36 a preferablyhas a modulus of elasticity between approximately 5×10⁴ pounds persquare inch and 1×10² pounds per square inch, and most preferably themodulus of elasticity is approximately 5×10³ pounds per square inch.

As best seen in FIG. 2, in accordance with the first embodiment, in anend elevation view thereof the optical module 30 a defines a generallyparallelogram-like shape having rounded corners. More specifically, asillustrated in FIGS. 1 and 2, the optical module 30 a is in a generallyrectangular configuration, which can also be characterized as anon-skewed configuration. For example, the optical module 30 a can becharacterized as being in the generally rectangular configurationbecause, as best seen in FIG. 2, angles of approximately ninety degreesare defined between the vertical and horizontal segments of the bufferencasement 36 a.

As shown in FIG. 2, a height “H” cross-dimension is defined betweenopposite top and bottom sides of the optical module 30 a. In addition, awidth “W” cross-dimension that is perpendicular to the height H isdefined between opposite right and left sides of the optical module 30a. As will be discussed in greater detail below with reference to FIGS.21 and 24-26, fiber optic cables having combinations of optical moduleswith different heights H and widths W are within the scope of thepresent invention.

Throughout this Detailed Description of the Invention section of thisdisclosure, items are described in the context of specific orientations,such as horizontal and vertical orientations. Those orientations areintended to provide a frame of reference to aid in the explanation ofthe present invention. The present invention can be described in thecontext of other orientations and is not limited to any specificorientation.

FIG. 3 is a perspective view of a representative optical fiber ribbon 34of the optical module 30 a (FIGS. 1 and 2). In accordance with thepresent invention, one acceptable design for the optical fiber ribbons34 is described in U.S. Pat. No. 4,900,126, which is incorporated hereinby reference. More specifically, each optical fiber ribbon 34 extendslongitudinally and includes a lateral array of conventional coatedoptical fibers 38 that transmit light. Whereas eight optical fibers 38are shown in FIG. 3, it is generally preferred for there to be twelve ortwenty-four optical fibers in each optical fiber ribbon 34, and it iswithin the scope of the present invention for each optical fiber ribbonto include a greater or lesser number of optical fibers.

Each optical fiber ribbon 34 further includes a solidified bondingmaterial 40 that fills the interstices between the optical fibers 38,binds together the optical fibers, and extends to the outside boundaryof the optical fiber ribbon 34. Each optical fiber ribbon 34 includes apair of opposite edges 42, 44 that extend in the longitudinal direction,and a pair of opposite flat lateral surfaces 46, 48 that extendlaterally between the edges 42, 44 and in the longitudinal direction.Referring back to FIG. 2, the generally rectangular configuration of theoptical module 30 a is further characterized by the flat lateralsurfaces 46, 48 (FIG. 3) of adjacent optical fiber ribbons 34 beingsubstantially entirely contiguous.

The solidified bonding material 40 (FIG. 3) is acceptably a knownultraviolet-curable matrix material that includes a resin, a diluent anda photoinitiator. The resin may include a diethylenic-terminated resinsynthesized from a reaction of hydroxy-terminated alkyl acrylate withthe reaction product of a polyester of polyethyl polyol of molecularweight of 1,000 to 6,000 with an aliphatic or aromatic diisocyanate, ordiethylenic-terminated resin synthesized from the reaction of glycidylacrylate with a carboxylic-terminated polymer or polyether of molecularweight 1,000 to 6,000. The diluent may include monofunctional ormultifunctional acrylic acid esters having a molecular weight of 100 to1,000 or N-vinylpyrrolidinone. For the photoinitiator, the compositionmay include ketonic compounds such as diethoxyacetophenone,acetophenone, benzophenone, benzoin, anthraquinone, and benzil dimethylketal. In a typical composition, the bonding matrix may include a resin(50-90%), diluents (5-40%), and a photoinitiator (1-10%). Allpercentages are by weight unless otherwise noted. Other bonding matricesmay include a methacrylate, an ultraviolet-curing epoxide or anunsaturated polyester.

FIG. 4 is an isolated end elevation view of the ribbon stack 32 a of theoptical module 30 a (FIGS. 1 and 2) in the generally rectangularconfiguration. That is, as illustrated in FIG. 4, the ribbon stack 32 adefines a generally rectangular shape and the flat lateral surfaces 46,48 (FIG. 3) of adjacent optical fiber ribbons 34 are substantiallyentirely contiguous. In FIG. 4, the ribbon stack 32 a is illustrated asincluding four optical fiber ribbons 34, with each of the optical fiberribbons containing eight optical fibers 38. In FIG. 4 only a few of theoptical fibers 38 are specifically identified with their referencenumeral. In accordance with the first embodiment, it is preferred forthe ribbon stack 32 a to be in the form of a stack of twelvelongitudinally extending optical fiber ribbons 34, with each opticalfiber ribbon including a laterally extending one-dimensional array oftwelve optical fibers 38. However, ribbon stacks 32 a containingdifferent numbers of optical fiber ribbons 34 and optical fiber ribbonscontaining different numbers of optical fibers 38 are within the scopeof the present invention.

In accordance with the first embodiment, the buffer encasement 36 a(FIGS. 1 and 2) may or may not be adhered to the ribbon stack 32 a. Asbest seen in FIG. 4, the ribbon stack 32 a has a top side 52, bottomside 54, right side 56, and left side 58. In accordance with anunadhered version of the first embodiment, which is most preferred, thebuffer encasement 36 a is not adhered to the sides 52, 54, 56, 58 of theribbon stack, so that the ribbon stack can move relative to the bufferencasement. As will be discussed in greater detail below, in accordancewith this unadhered version, each of the sides 52, 54, 56, 58 islubricated, in contact with the interior surface of the bufferencasement 36 a, and can move longitudinally relative to the bufferencasement. In contrast, in accordance with an adhered version of thefirst embodiment, the buffer encasement 36 a is adhered to the sides 52,54, 56, 58 of the ribbon stack 32 a, so that the ribbon stack isrestricted from moving relative to the buffer encasement.

As best seen in FIG. 4, in accordance with the first embodiment,interstices 50 that are arranged along the right and left sides 56, 58of the ribbon stack 32 a are defined between the edges 42, 44 (FIG. 3)of adjacent optical fiber ribbons 34. As best seen in FIG. 2, inaccordance with the illustrated version of the first embodiment,interstices 50 are not filled by the buffer encasement 36 a. Inaccordance with another version of the first embodiment, the interstices50 are filled by the buffer encasement 36 a. Whether or not theinterstices 50 are filled by the buffer encasement 36 a generallydepends on the method by which, and the material from which, the bufferencasement is formed. As will be discussed in greater detail below,numerous methods for forming the buffer encasement 36 a are within thescope of the present invention.

As shown in FIG. 4, each optical fiber ribbon 34 defines approximatelythe same thickness T1. As best seen in FIG. 6, which is an isolated endelevation view of the buffer encasement 36 a of the optical module 30 a(FIGS. 1 and 2) in the rectangular configuration, the buffer encasement36 a can be characterized as including four separate walls, each ofwhich defines approximately the same thickness T2. In accordance withthe first embodiment, the thickness T1 (FIG. 4) of each of the opticalfiber ribbons 34 (FIGS. 1-3) is preferably at least approximately asgreat as the thickness T2 of the buffer encasement 36 a. Stated morespecifically and differently, in accordance with the first embodiment inthe entirety of the buffer encasement 36 a has a thickness ofapproximately T2 that is preferably not greater than the thickness T1 ofeach optical fiber ribbon 34. In accordance with the first embodiment,the thickness T1 of each optical fiber ribbon 34 is approximately 0.012to 0.02 inches, or most preferably approximately 0.012 inches. Inaccordance with the first embodiment, the thickness T2 of the bufferencasement 36 a is approximately 0.003 to 0.012 inches, or morepreferably approximately 0.007 to 0.012 inches, or most preferablyapproximately 0.008 to 0.009 inches.

FIG. 5 is an end elevation view of the optical module 30 a in a skewedconfiguration, in accordance with the first embodiment. For example, theoptical module 30 a can be characterized as being in the skewedconfiguration because oblique angles are defined between the generallyvertical and horizontal segments of the buffer encasement 36 a, and thelateral surfaces 46, 48 (FIG. 3) of adjacent optical fiber ribbons 34are not entirely contiguous. That is, adjacent optical fiber ribbons 34are at least partially laterally displaced from one another. Because thebuffer encasement 36 a is constructed of a relatively thin flexiblematerial, the optical fiber ribbons 34 are capable of sliding laterallyrelative to one another when oppositely oriented lateral forces areapplied against the optical module 30 a, so that the optical moduletransitions from the generally rectangular configuration (FIGS. 1 and 2)to the skewed configuration. That is, the buffer encasement 36 a isconstructed and arranged to be flexible enough to allow the opticalfiber ribbons 34 to slide laterally relative to one another so that, inan end elevation view thereof, the stack can transition from anapproximately rectangular arrangement to the skewed configuration. Thebuffer encasement 36 a is further constructed and arranged to be rigidenough to maintain the stack of optical fiber ribbons 34 in a stackedconfiguration when the optical module 30 a is transitioned from thegenerally rectangular configuration to the skewed configuration.Further, the buffer encasement 36 a is constructed and arranged so thatthe optical module 30 a is biased toward the generally rectangularconfiguration.

In accordance with the illustrated version of the first embodiment, theability of the optical module 30 a to be readily transitioned betweenthe generally rectangular configuration (FIGS. 1 and 2) and the skewedconfiguration (FIG. 5) is enhanced by virtue of the interstices 50 (FIG.4) defined between the edges 42, 44 (FIG. 3) of adjacent optical fiberribbons 34 not being filled by the buffer encasement 36 a. Further, inaccordance with the unadhered version of the first embodiment, a coatingof lubricant (not shown), such as oil or the like, as will be discussedin greater detail below, is upon the edges 42, 44 and lateral surfaces46, 48 (FIG. 3) of each of the optical fiber ribbons 34. The lubricantenhances the ability of the optical fiber ribbons 34 to be movedlaterally and longitudinally relative to one another and relative to thebuffer encasement 36 a. Therefore, the lubricant enhances the ability ofthe optical module 30 a to be transitioned between the generallyrectangular configuration and the skewed configuration.

As best seen in FIG. 6, the buffer encasement 36 a includes an interiorsurface 60 a and an exterior surface 62 a. The interior surface 60 aextends around and defines a longitudinally extending passage 64. Inaccordance with the first embodiment, in both the generally rectangularconfiguration (FIGS. 1 and 2) and the skewed configuration (FIG. 5), theinterior surface 60 a closely bounds the periphery of the ribbon stack32 a (FIGS. 1, 2, and 3) and the exterior surface 62 a closely boundsthe interior surface. The close bounding of the interior and exteriorsurfaces 60 a, 60 b provides for efficient packaging of multiple of theoptical modules 30 a (FIGS. 1, 2, and 5), as will be discussed ingreater detail below. More specifically, in an end elevation view of theoptical module 30 a during both the generally rectangular configurationand the skewed configuration, the interior surface 60 a defines a shapethat is substantially similar to the shape defined by the periphery ofthe ribbon stack 32 a (FIGS. 1, 2, 4, and 5), with substantially theonly difference between the shapes being that the interstices 50 (FIG.4) are not filled by the buffer encasement 36 a. In addition, in the endelevation view of the optical module 30 a during both the generallyrectangular configuration and the skewed configuration, the exteriorsurface 62 a also defines a shape that is substantially similar to theshape defined by the periphery of the ribbon stack 32 a, withsubstantially the only difference between the shapes being that theinterstices 50 are not filled by the buffer encasement 36 a. In both thegenerally rectangular configuration and the skewed configuration, in theend elevation view of the optical module 30 a, the periphery of theribbon stack 32 a bounds a first area and the interior surface of thebuffer encasement 36 a bounds a second area, and the first and secondareas are approximately equal.

In accordance with a first version of the first embodiment, the bufferencasement 36 a is homogenous, meaning that all portions of the bufferencasement have approximately the same properties, such as hardness andmodulus of elasticity. As best understood with reference to FIG. 6, inaccordance with a second version of the first embodiment, the bufferencasement 36 a has an inner portion 68a and an outer portion 70 a thatare preferably not physically separate from one another but that havedifferent properties, such as hardness and modulus of elasticity.Although there is not necessarily a clearly visible distinction betweenthe inner and outer portions 68 a, 70 a with the naked eye and thetransition between the inner and outer portions may be gradual, forpurposes of explanation a separation line 66 is illustrated by brokenlines in FIG. 6 to demonstrate a boundary between the inner and outerportions. In accordance with the second version of the first embodiment,the outer portion 70 a has a hardness and modulus of elasticity that aregreater than the hardness and modulus of elasticity of the inner portion68 a. More specifically, in accordance with the second version of thefirst embodiment, the inner portion 68 a of the buffer encasement 36 apreferably has a modulus of elasticity between approximately 2×10⁴pounds per square inch and 1×10² pounds per square inch, and mostpreferably the modulus of elasticity of the inner portion isapproximately 1×10³ pounds per square inch. In contrast, in accordancewith the second version of the first embodiment, the outer portion 70 aof the buffer encasement 36 a preferably has a modulus of elasticitybetween approximately 6×10⁵ pounds per square inch and 2×10⁴ pounds persquare inch, and most preferably the modulus of elasticity of the outerportion is approximately 2×10⁵ pounds per square.

In accordance with the first embodiment, it is preferred for the opticalfibers 38 and the optical fiber ribbons 34 to be conventionallycolor-coded or marked with identifying indicia, or the like, foridentification purposes. It is preferred for the buffer encasement 36 ato be clear so that the identifying colors or markings of the opticalfiber ribbons 34 and/or optical fibers 38 can be seen through the bufferencasement. Alternatively or in addition, different buffer encasements36 a are color-coded or marked with identifying indicia, or the like,for identification purposes.

In accordance with a version of the first embodiment, the bufferencasement 36 a can be easily torn so that the buffer encasement can beeasily removed from the ribbon stack 32 a. In accordance with oneexample of this easily torn version, the buffer encasement 36 a has anultimate tensile strength of less than approximately 2×10³ pounds persquare inch and a thickness T2 (FIG. 6) of less than approximately 0.020inches. In accordance with this example of the easily torn version, thebuffer encasement 36 a is acceptably constructed of low-densitypolyethylene, or the like.

In accordance with another example of the easily torn version, thebuffer encasement 36 a is easily tearable because it is constructed of apolymeric material that contains one or more fillers, such as inorganicfillers, that reduce the elongation and/or tensile strength of thepolymeric material. Preferably this easily tearable buffer encasementhas a tensile strength of less than approximately 2,000 pounds persquare inch, an elongation of less than approximately 400 percent, andmost preferably less than approximately 200 percent. In accordance withthis example, suitable base resins or polymers include polyethylene,ethylene-vinyl acetate, ethylene-acrylic acid, or the like. Inaccordance with this example, suitable fillers include talc, calciumcarbonate, aluminum trihydrate, or the like.

Second Embodiment

FIG. 7 is a perspective view of an optical module 30 b in accordancewith a second embodiment of the present invention. The optical module 30b of the second embodiment is identical to the optical module 30 a(FIGS. 1, 2, and 5) of the first embodiment, except for noted variationsand variations apparent to those of ordinary skill in the art.

In accordance with the second embodiment, the ribbon stack 32 b of theoptical module 30 b is longitudinally twisted when its buffer encasement36 b is formed therearound, and the buffer encasement 36 b issufficiently rigid to hold the ribbon stack 32 b in its twistedconfiguration. In addition, as described above for the first embodiment,the buffer encasement 36 a of the second embodiment is relatively thinand conforms closely to the exterior surface of the ribbon stack 32 a.As a result, the longitudinally extending four corners 71 of the bufferencasement 36 a are arranged so as to define a longitudinal twist thatcorresponds to the twist of the ribbon stack 32 b, as is shown in FIG.7. That is, the exterior surface 62 b of the buffer encasement 36 bdefines ridgelike corners 71, which can be characterized as ridges, thatdefine a lay length that corresponds to the lay length of the twistedribbon stack 32 b. The corners 71 are preferably somewhat rounded.

The optical module 30 b can have a continuous helical twist or an S-Ztwist. More specifically, the ribbon stack 32 b can be longitudinallytwisted in the same direction for the entire length of the bufferencasement 36 b to provide the continuous helical twist. In contrast, itis preferred for the longitudinal twisting of the ribbon stack 32 b tobe periodically reversed, so that the optical module 30 b has what isreferred to by those of ordinary skill in the art as an S-Z twist. Inthis regard, along a first section of the buffer encasement 36 b theribbon stack 32 b is longitudinally twisted in a first direction todefine a lay length, and the ribbon stack is longitudinally twisted inan opposite second direction along a contiguous second section of thebuffer encasement to again define the lay length. The lay length is thelongitudinal distance in which the ribbon stack 32 b makes a completerevolution. That alternating twisting pattern is repeated along theentire length of the ribbon stack 30 b. In accordance with the secondembodiment, the lay length of the S-Z twist is preferably in the rangeof approximately twelve to thirty-six inches, and most preferably thelay length is approximately twenty-four inches.

Third Embodiment

FIG. 8 is an end elevation view of an optical module 30 c in accordancewith a third embodiment of the present invention. The optical module 30c of the third embodiment is identical to the optical module 30 a (FIGS.1, 2, and 5) of the first embodiment, except for noted variations andvariations apparent to those of ordinary skill in the art.

In accordance with the third embodiment, the buffer encasement 36 cdefines a longitudinally extending weakened portion. The weakenedportion preferably extends for the length of the optical module 30 c andis preferably in the form of a longitudinally extending frangibleportion 72. Whereas the frangible portion 72 is shown in the form of atrough-like cutout, the frangible portion can be in the form of a seriesof perforations or other voids or means that weaken the bufferencasement 36 c. The buffer encasement 36 c can be manuallylongitudinally torn along the frangible portion 72 more easily than thebuffer encasement can be torn at other locations. Nonetheless, thefrangible portion 72 is preferably constructed and arranged so that itdoes not tear inadvertently.

The frangible portion 72 is longitudinally torn to provide access to theoptical fiber ribbons 34 contained within the buffer encasement 36 c.More specifically, by tearing the buffer encasement 36 c along thefrangible portion 72, opposite longitudinally extending torn edges 74,76, which are illustrated by broken lines in FIG. 8, are formed. Thetorn edges 74, 76 are manually lifted away from the optical fiberribbons 34 contained by the buffer encasement 36 c so that alongitudinally extending opening 78 c is defined between the torn edges,as is illustrated by broken lines in FIG. 8. The optical fiber ribbons34 contained by the buffer encasement 36 c can be accessed through theopening 78 c. In accordance with an alternative embodiment of thepresent invention, the buffer encasement 36 c is constructed of amaterial that can be easily torn so that the buffer encasement can bereadily manually longitudinally torn without including a frangibleportion 72.

Fourth Embodiment

FIG. 9 is an end elevation view an optical module 30 d in accordancewith a fourth embodiment of the present invention. The optical module 30d of the fourth embodiment is identical to the optical module 30 a(FIGS. 1, 2, and 5) of the first embodiment, except for noted variationsand variations apparent to those of ordinary skill in the art.

In accordance with the fourth embodiment, the buffer encasement 36 d ispreferably a longitudinally extending piece of polymeric film or tape.The tape preferably cannot be penetrated by water and/or may be coatedwith a conventional powder that absorbs water, or the like. The bufferencasement 36 d includes opposite longitudinally extending edges 80, 82that overlap one another so the optical fiber ribbons 34 are enclosedwithin the buffer encasement.

The surfaces of the edges 80, 82 that are overlapping and facing oneanother are preferably held together by a conventional adhesive so thatthose edges remain in their overlapping arrangement. In accordance withthe unadhered version of the fourth embodiment, the adhesive does notcover the entire interior surface of the buffer encasement 36 d so theoptical fiber ribbons 34 contained by the buffer encasement can moverelative to one another and relative to the buffer encasement. Inaccordance with the adhered version of the fourth embodiment, the entireinterior surface of the buffer encasement 36 d is be covered by theadhesive so that movement of the optical fiber ribbons 34 relative toone another as well as relative to the buffer encasement is impeded.

In accordance with the fourth embodiment, when access to the opticalfiber ribbons 34 within the buffer encasement 36 c is desired, the edges80, 82 are manually separated to provide access to the optical fiberribbons within the buffer encasement. More specifically, the separatededges 80, 82 are lifted away from the optical fiber ribbons 34 containedby the buffer encasement 36 d so that a longitudinally extending opening78 d is defined between the edges, as is illustrated by broken lines inFIG. 9. The optical fiber ribbons 34 contained by the buffer encasement36 d can be accessed through the opening 78 d. In addition, the edges80, 82 can be returned to their original configurations to again fullyenclose the optical fiber ribbons 34, if desired.

In accordance with an alternative embodiment of the present invention,the polymeric tape or sheet from which the buffer encasement 36 d isconstructed is wrapped helically around the optical fiber ribbons 34 toform the buffer encasement, rather than being longitudinally applied tothe optical fiber ribbons.

Fifth Embodiment

FIGS. 10 and 11 are perspective and end elevation views, respectively,of an optical module 30 e in accordance with a fifth embodiment of thepresent invention. The optical module 30 e of the fifth embodiment isidentical to the optical module 30 a (FIGS. 1, 2, and 5) of the secondversion of the first embodiment, which is discussed above with referenceto FIG. 6, except for noted variations and variations apparent to thoseof ordinary skill in the art.

In accordance with the fifth embodiment, the buffer encasement 36 e hasmultiple plies. More specifically, the inner and outer portions 68 e, 70e are separate plies. The inner portion 68 e includes an outer surface86 e and the outer portion 70 e includes an inner surface 88 e. Inaccordance with the fifth embodiment, the entire inner surface 88 eextends around and is in contact with the entire outer surface 86 e forthe entire length of the optical module 30 e. In accordance with a firstversion of the fifth embodiment, the inner and outer portions 68 e, 70 eare coaxial thermoplastic coextrusions. In accordance with a secondversion of the fifth embodiment, the inner portion 68 e is like thetapes or films described above with reference to the fourth embodiment,and the outer portion 70 e is a polymeric extrusion, with the thicknessof the multi-ply buffer encasement 36 e being identical to the thicknessT2 (FIG. 6) of the buffer encasement 36 a (FIGS. 1, 2, and 5) of thefirst embodiment. Alternatively the thickness of the multi-ply bufferencasement 36 e is greater than the thickness of the buffer encasement36 a of the first embodiment. A third version of the fifth embodiment isidentical to the second version of the fifth embodiment, except thatboth the inner portion 68 e and the outer portion 70 e are like thetapes or films described above with reference to the fourth embodiment.

Sixth Embodiment

FIGS. 12 and 13 are perspective and end elevation views, respectively,of an optical module 30 f in accordance with a sixth embodiment of thepresent invention. The optical module 30 f of the sixth embodiment isidentical to the optical module 30 a (FIGS. 1, 2, and 5) of the firstembodiment, except for noted variations and variations apparent to thoseof ordinary skill in the art.

As best seen in FIG. 13, in accordance with the illustrated version ofthe sixth embodiment, the interstices 50 (FIG. 4) defined between theedges 42, 44 (FIG. 3) of the optical fiber ribbons 34′ are filled byportions of the buffer encasement 36 f. In addition, the bufferencasement 36 f includes thickened portions 90 at the opposite fourcorners thereof. The thickened portions 90 preferably definebulbous-like shapes that cushion the optical fibers positioned at theopposite four corners of the ribbon stack 32 f. Except for the thickenedportions 90, the thickness of the buffer encasement 36 f is identical tothe thickness T2 (FIG. 6) of the buffer encasement 36 a (FIGS. 1, 2, 5,and 6) of the first embodiment. Accordingly, a vast majority of thebuffer encasement 36 f has a thickness defined between the interior andexterior surfaces thereof that is not greater than the thickness of eachof the optical fiber ribbons 34′ contained by the buffer encasement 36f.

Seventh Embodiment

FIG. 14 is an end elevation view of an optical module 30 g in accordancewith a seventh embodiment of the present invention. The optical module30 g of the seventh embodiment is identical to the optical module 30 a(FIGS. 1, 2, and 5) of the first embodiment, except for noted variationsand variations apparent to those of ordinary skill in the art.

The optical module 30 g is illustrated in the non-skewed configurationin FIG. 14 and therefore can be characterized as including a generallyround ribbon stack 32 g and a round buffer encasement 36 g. In contrast,the ribbon stack 32 g and the buffer encasement 36 g may be oblong in anend elevation view thereof while the optical module 30 g is in theskewed configuration. The optical fiber ribbons 34, 34′, 34″, 34′″, 34″″of the ribbon stack 32 g have different widths, and some of the opticalfiber ribbons are in a side-by-side arrangement. In addition, thethickness of the buffer encasement 36 g is measured in the direction ofradii that radiate from the center of the optical module 30 g in an endelevation view thereof. Whereas that thickness varies with the angle ofthe radii, the average thickness of the buffer encasement 36 gcorresponds to the thickness T2 (FIG. 6) of the buffer encasement 62 a(FIGS. 1, 2, 5, and 6) of the first embodiment. That is, a majority ofthe buffer encasement 36 g has a thickness defined between the interiorand exterior surfaces thereof that is not greater than the thickness(for example see the thickness T1 illustrated in FIG. 4) of each of theoptical fiber ribbons 34, 34′, 34″, 34′″, 34″″ contained by the bufferencasement 36 g.

Methods of Manufacturing Optical Modules

FIG. 15 diagrammatically illustrates an assembly of manufacturingequipment 92 that is capable of acceptably manufacturing opticalmodules, such as the above-discussed optical modules 30 a, 30 b, 30 c,30 d, 30 e, 30 f, 30 g of the present invention. For the purpose ofdescribing methods of operation of the assembly of manufacturingequipment 92, the above-described optical modules, ribbon stacks, andbuffer encasements are referred to generically as optical module 30,ribbon stack 32, and buffer encasement 36. The assembly of manufacturingequipment 92 operates such that the optical fiber ribbons 34 and theformed ribbon stack 32, buffer encasement 36, and optical module 30 arecontinuously longitudinally advanced.

Upstream Guiding Mechanism

As seen in FIG. 15, separate optical fiber ribbons 34 are drawn inparallel into an upstream guiding mechanism 94. Whereas only fouroptical fiber ribbons 34 are illustrated in FIG. 15, it is within thescope of the present invention for more and less than four optical fiberribbons to be drawn into the assembly of manufacturing equipment 92. Theprocess of feeding the optical fiber ribbons 34 to the upstream guidingmechanism 94 preferably includes conventionally dispensing previouslymanufactured optical fiber ribbons 34, such as dispensing the opticalfiber ribbons from reels that are positioned upstream from the upstreamguiding mechanism.

In accordance with one example of the present invention, the guidingmechanism 94 includes multiple rollers, or the like, that defined nipsthrough which the optical fiber ribbons 34 are drawn for generallyaligning the optical fiber ribbons with one another and maintainingspaces between the optical fiber ribbons. It is conventional to drawoptical fiber ribbons into a parallel arrangement, so the operations ofthe upstream guiding mechanism 94 should be understood by those ofordinary skill in the art.

Lubricating Mechanism

As illustrated in FIG. 15, the aligned optical fiber ribbons 34 aredrawn from the upstream guiding mechanism 94 to a lubricating mechanism96. The lubricating mechanism 96 applies lubricant to the edges 42, 44(FIG. 3) and the lateral surfaces 46, 48 (FIG. 3) of each of the opticalfiber ribbons 34. The lubricant can be acceptably applied to the opticalfiber ribbons 34 by any of numerous conventional coating techniques. Forexample, liquid lubricant can be applied to the optical fiber ribbons 34by a spraying assembly including pump(s) that force liquid lubricant toflow from a reservoir, through piping, and out of spray nozzles thatdirect the lubricant onto the optical fiber ribbons 34. An example of anassembly for applying lubricant to optical fiber ribbons is disclosed inU.S. patent application Ser. No. 09/179,721, which is incorporatedherein by reference. In addition, the optical fiber ribbons 34 can bedrawn through a bath of the lubricant, or drawn between absorbentrollers that are saturated with the lubricant. Alternatively,powder-type lubricants can be sprinkled and blown onto the optical fiberribbons 34.

It is preferred for the applied lubricant not to adversely interact withthe optical fiber ribbons 34 or the buffer encasement 36 formed aroundthe optical fiber ribbons. For example, it is preferred for thelubricant not to cause the buffer encasement 36 to swell. For example,in accordance with some embodiments of the present invention “E”-typehydrocarbon oils are used when the buffer encasement 36 is constructedof a low density polyethylene material. Specifically, “E”-typehydrocarbon oil comprises 22.5% by weight of SHF-402 polyalphaolefinoil; 75.5% by weight of SHF-82 polyalphaolefin oil; and 2% by weight ofIRGANOX® 1076 antioxidant. These polyalphaolefin oils are commerciallyavailable from Mobil Chemical Company, and the antioxidant (stabilizer)is commercially available from the Ciba-Geigy Company. This oil has aviscosity between 54 and 82 centistrokes at 40° C., and a viscositybetween 8 and 12 centistrokes at 100° C. when measured in accordancewith the method of ASTM D-445. These oils were selected to have akinematic viscosity that is less than 4000 centistrokes at 100° C.

In accordance with other embodiments of the present invention a morepolar oil, such as glycol, is used when the buffer encasement 36 isconstructed of ethylene-vinyl acetate copolymer. It is also preferredfor the lubricant that is applied to the optical fiber ribbons 34 to bewater resistant or contain a water absorbent powder, or the like. For amajority of the embodiments of the present invention, including thesecond embodiment, a preferred lubricant is stabilized polyalphaolefinoil, or the like. Other suitable lubricants include glycol, siliconeoils, or the like.

It is also within the scope of the present invention for the assembly ofmanufacturing equipment 92 not to include the lubricating mechanism 96.For example, it is within the scope of the present invention for theoptical fiber ribbons 34 of an optical module 30 to not be lubricated,such as for the unadhered versions of the optical module discussed abovewith reference to the first embodiment.

Downstream Guiding Mechanism

As illustrated in FIG. 15, the optical fiber ribbons 34 are drawn fromthe lubricating mechanism 96 to a downstream guiding mechanism 98. Thedownstream guiding mechanism 98 includes multiple rollers that guide theoptical fiber ribbons 34 so that the optical fiber ribbons are formedinto a ribbon stack 32. It is conventional to arrange optical fiberribbons 34 into a ribbon stack 32, so the operations of the downstreamguiding mechanism 98 should be understood by those of ordinary skill inthe art.

Twisting Mechanism

The assembly of manufacturing equipment 92 is illustrated as furtherincluding a twisting mechanism 99. In accordance with those embodimentsof the present invention in which the ribbon stack 32 is twisted, theribbon stack 32 is drawn from the downstream guiding mechanism 98 to thetwisting mechanism 99. The twisting mechanism 99 is operative to imparteither a continuous helical twist in the ribbon stack 32 or an S-Ztwist, as described above with reference to the second embodiment of thepresent invention.

It is preferred, when practicable, for many of the optical modules 30 ofthe present invention to be constructed so that their ribbon stacks 32are S-Z twisted. For example, in accordance with alternative embodimentsof the present invention, optical modules 30 similar to the opticalmodules 30 a (FIGS. 1, 2, and 5), 30 c (FIG. 8), 30 d (FIG. 9), and 30 e(FIGS. 10 and 11), and discussed variants thereof, have twisted ribbonstacks 32.

It is conventional to longitudinally twist ribbon stacks 32, so theoperations of the twisting mechanism 99 should be understood by those ofordinary skill in the art. An acceptable example of a twisting mechanismis disclosed in U.S. patent application Ser. No. 09/179,721, which hasbeen incorporated herein by reference. In accordance with embodiments ofthe present invention in which the ribbon stack 32 is twisted, theribbon stack is drawn from the twisting mechanism 99 to the encasingmechanism 100.

In accordance with some of the embodiments of the present invention, theribbon stack 32 is not twisted, in which case the twisting mechanism 99is bypassed or omitted from the assembly of manufacturing equipment 92.That is, in accordance with embodiments of the present invention inwhich the ribbon stack 32 is not twisted, the ribbon stack is drawn fromthe downstream guiding mechanism 98 to an encasing mechanism 100.

Encasing Mechanism

The encasing mechanism 100 forms the buffer encasement 36 around theribbon stack 32 to form the optical module 30. Multiple variations ofthe encasing mechanism 100 are within the scope of the presentinvention, and examples of them will be briefly described, followed by amore detailed discussion of each. In accordance with a first method ofthe present invention, the encasing mechanism 100 applies a polymerictape or film to the ribbon stack 32 to form the buffer encasement 36. Inaccordance with a second method of the present invention, the encasingmechanism 100 extrudes thermoplastic material around the ribbon stack 32to form the buffer encasement 36. In accordance with a third method ofthe present invention, the encasing mechanism 100 applies anultraviolet-curable material onto the ribbon stack 32 and cures thatmaterial to form the buffer encasement 36. In accordance with a fourthmethod of the present invention, the encasing mechanism 100 performs theabove operations in various combinations and subcombinations to providecomposite buffer encasements 36.

First Method: In accordance with the first method of the presentinvention, the buffer encasement 36 is formed by way of the encasingmechanism 100 applying a longitudinally extending polymeric tape or filmto the ribbon stack 32, or helically wrapping the tape or film aroundthe ribbon stack to produce an optical module 30. It is conventional inthe construction of fiber optic cables to apply a longitudinallyextending tape to a longitudinally advancing member, and to helicallywrap tape around a longitudinally advancing member, so those of ordinaryskill in the art should be able to select a suitable encasing mechanism100 for carrying out the first method.

Optical modules 30 constructed in accordance with the first methodinclude those described above with reference to the fourth embodimentand variations thereof. It is also within the scope of the presentinvention for other optical modules 30 to be constructed in accordancewith the first method.

In accordance with the first method, the tapes or films from which thebuffer encasement 36 is constructed are acceptably constructed fromthermoplastic materials, or more specifically polyolefin materials, ormore specifically polyethylene. In accordance with the fourth embodimentdiscussed above, a particularly suitable tape is conventionalwater-blocking tape with conventional nonwoven polyester backing.

Second Method: In accordance with the second method of the presentinvention, the encasing mechanism 100 includes one or more extrudersthat extrude the buffer encasement 36 over the ribbon stack 32. It isconventional in the construction of fiber optic cables to utilize anextruder to extrude a thermoplastic material onto a longitudinallyadvancing member, so those of ordinary skill in the art should be ableto select a suitable encasing mechanism 100 for carrying out the secondmethod.

In accordance with the second method, the material being extruded isacceptably a thermoplastic material, or more specifically a polyolefinmaterial, or more specifically polyethylene. Further, in accordance withthe second method, the extrusion(s) may be sufficiently solidifiedthrough exposure to the ambient air. Alternatively or in addition, theencasing mechanism 100 can include cooling mechanism(s) that aid in thecooling and solidification of the extrusion(s). Acceptable coolingmechanisms include water baths, or the like.

In accordance with a first version of the second method, the encasingmechanism 100 extrudes a thermoplastic extrusion around the ribbon stack32, and that extrusion solidifies to form the buffer encasement 36. Morespecifically, the initially formed extrusion has internal dimensionsthat are larger than the external dimensions of the ribbon stack 32, andas the extrusion solidifies the extrusion is “drawn down” to the ribbonstack 32 to form the buffer encasement 36. As a result of the drawingdown, the internal dimensions of the buffer encasement 36 areapproximately equal to the external dimensions of the ribbon stack 32.For example, the optical module 30 a (FIGS. 1, 2 and 5) of the firstversion of the first embodiment and the optical modules 30 b, 30 c ofthe second and third embodiments, respectively, can be constructed inaccordance with the first version of the second method. In accordancewith the first version of the second method, a particularly suitablematerial for extruding to form the buffer encasements 36, and thematerial that is preferably used to construct the buffer encasement 36 b(FIG. 7) of the second embodiment, is low-density polyethylene, or thelike.

Second and third versions of the second method are similar to the firstversion of the second method, except in accordance with the second andthird versions the encasing mechanism 100 forms thermoplasticcoextrusions around the ribbon stack 32. In accordance with the secondversion of the second method, the facing surfaces of the coextrusionspartially blend together before solidifying, for example to produce thenonhomogenous buffer encasement 36 a (FIG. 6) of the second version ofthe first embodiment. In accordance with the second version of thesecond method, a preferred material for extruding to form the innerportion 68 a (FIG. 6) of the buffer encasement 36 a is very low densitypolyethylene-vinyl acetate, ethylene-acrylic acid, or the like. Inaccordance with the second version of the second method, a preferredmaterial for extruding to form the outer portion 70 a (FIG. 6) of thebuffer encasement 36 a is medium or high density polyethylene, or thelike.

In accordance with the third version of the second method, thecoextrusions do not partially blend together before solidifying, forexample to produce the buffer encasement 36 e (FIGS. 10 and 11) of thefifth embodiment. In accordance with the third version of the secondembodiment, a preferred material for extruding to form the inner portion68 e (FIGS. 10 and 11) of the buffer encasement 36 e is very low densitypolyethylene, ethylene-vinyl acetate, ethylene-acrylic acid, or thelike. In accordance with the third version of the second embodiment, apreferred material for extruding to form the outer portion 70 e (FIGS.10 and 11) of the buffer encasement 36 e is impact modifiedpolypropylene (propylene-ethylene copolymer), or the like.

Third Method: In accordance with the third method of the presentinvention, the encasing mechanism 100 applies an uncuredultraviolet-curable material onto and around the ribbon stack 32 andthereafter cures the ultraviolet-curable material to form the bufferencasement 36 around the ribbon stack. The ultraviolet-curable materialis cured by exposure to ultraviolet radiation. As mentioned above, it isconventional to use ultraviolet-curable materials is the construction ofoptical fiber ribbons 34, so those of ordinary skill in the art shouldbe able to select a suitable encasing mechanism 100 for carrying out thethird method.

In accordance with the third method, the uncured ultraviolet-curablematerial can be applied to the ribbon stack 32 through the use ofseveral different techniques. For example, the uncuredultraviolet-curable material can be extruded onto the ribbon stack 32,sprayed onto the ribbon stack, or the ribbon stack can be drawn througha bath of the uncured ultraviolet-curable material. Thereafter, theuncured ultraviolet-curable material on the ribbon stack 32 is cured byexposure to ultraviolet radiation.

Optical modules 30 constructed in accordance with the third methodinclude those described above with reference to the sixth and seventhembodiments. For example, when constructing the optical module 30 f(FIGS. 12 and 13) of the sixth embodiment, preferably a thickultraviolet-curable material is extruded onto the ribbon stack 32 f(FIGS. 12 and 13), and the die that is used for the extruding isconstructed and arranged to define the shape of the resulting bufferencasement 36 f (FIGS. 12 and 13).

In accordance with the third method, buffer encasements 36 having innerand outer portions, such as inner and outer portions 68 a, 70 a (FIG.6), with different properties can be produced by controlling theapplication of the ultraviolet radiation to the uncuredultraviolet-curable material that has been applied to the ribbon stack32. For example, a homogenous ultraviolet-curable gel can be applied toa ribbon stack 32 and then the duration and intensity of the ultravioletradiation imparted on the applied ultraviolet-curable material iscontrolled so the resulting buffer encasement 36 has an inner portionand an outer portion, such as inner and outer portions 68 a, 70 a,having different hardness and modulus of elasticity. For example, it ispreferred for the inner portion to be softer and have a lower modulus ofelasticity, and for the outer portion to be harder and have a highermodules of elasticity, as described above with reference to the secondversion of the first embodiment. That is, the forming of the bufferencasement 36 is carried out by coating the stack of optical fiberribbons 34 with the ultraviolet-curable material and thereafter exposingthe ultraviolet-curable material to ultraviolet radiation for apredetermined period of time selected so that on a per unit basis morecuring, such as polymerization, occurs in the outer portion 70 a thanthe inner portion 68 a.

A suitable ultraviolet-curable material is that which is described aboveas being used in the formation of the optical fiber ribbons 34. Othersuitable ultraviolet-curable materials include acrylate materials thatare polymerized when exposed to ultraviolet radiation to createpolyacrylate.

Fourth Method: In accordance with the fourth method of the presentinvention, the first, second, and third methods are combined and/orvaried to produce other optical modules 30. For example, in accordancewith the second version of the fifth embodiment, the inner portion 68 e(FIGS. 10 and 11) is constructed of a tape or film of polymeric materialthat blocks water, and the outer portion 70 e (FIGS. 10 and 11) is anextrusion of polymeric material.

Weakening Mechanism

In accordance with embodiments of the present invention in which thebuffer encasement 36 includes a frangible portion 72 (FIG. 8), or thelike, the optical module is drawn from the encasing mechanism 100 to aweakening mechanism 101. The weakening mechanism 101 forms alongitudinally extending frangible portion, such as the illustratedfrangible portion 72, in the buffer encasement 36. Suitable frangibleportions can be formed through the use of a wide variety of devices,such as cutting, scoring, or piercing devices, or the like.

In accordance with the third embodiment, the weakening mechanism 101 ispreferably a machine that generates a laser beam that is used to cut thebuffer encasement 36 c (FIG. 8) to form the frangible portion 72 (FIG.8). Cutting machines that form precise cuts by means of a laser areconventional and readily available

Storing Mechanism

As illustrated in FIG. 15, the completely manufactured optical module 30is drawn to a conventional storing mechanism 102. A suitable storingmechanism can include a reel that the manufactured optical module 30 isdrawn onto and wrapped around. Optical modules 30 that have beenlongitudinally twisted, such as the optical module 30 b (FIG. 7) andround optical modules, such as the optical module 30 g (FIG. 14), areparticularly well suited for being wound onto reels. Alternatively, thestoring mechanism 102 can include barrels that the manufactured opticalmodules 30 are continuously drawn toward and dropped into.

Irrespective of the manner in which an optical module 30 is stored, itis preferred for the opposite ends of the optical module to be readilyavailable so that the optical integrity of the optical module can betested prior to incorporating the optical module into a fiber opticcable. This is particularly advantageous with respect to fiber opticcables that include multiple optical modules 30 in parallel.

Fiber Optic Cables

FIGS. 16-21 and 24-26 illustrates fiber optic cables in accordance withembodiments of the present invention. For the purpose of describing thefiber optic cables, the above-described optical modules 30 a, 30 b, 30c, 30 d, 30 e, 30 f, 30 g of the present invention are referred togenerically as optical modules 30, because it is within the scope of thepresent invention for each of the below-described fiber optic cables,and/or variations thereof, to be constructed with each of theabove-described optical modules and combinations thereof, withexceptions being noted or apparent to those of ordinary skill in theart. Likewise, the above-described ribbon stacks and buffer encasementsare respectively referred to generically as ribbon stacks 32 and bufferencasements 36.

Eighth Embodiment

FIG. 16 is a schematic end elevation view of a fiber optic cable 108 ain accordance with an eighth embodiment of the present invention. Thefiber optic cable 108 a includes a centrally located and longitudinallyextending optical module 30 that is preferably surrounded by aconventional, longitudinally extending piece of water-blocking tape 110.A conventional outer jacket of polymeric material 112 a extends aroundthe water-blocking tape 110 and longitudinally extending outer strengthmembers 114 a are embedded in the outer jacket. The space between thewater-blocking tape 110 and the optical module 30, as well as the spacebetween the outer jacket 112 a and the water-blocking tape, can befilled with a conventional filler material, such as a thixotropic gel.It is preferred for each of the fiber optic cables of the presentinvention not to include any filler materials, such as thixotropic gels,but it is also within the scope of the present invention for each of thefiber optic cables of the present invention to include filler materials,such as thixotropic gels. In accordance with the present invention, itis preferred for the buffer encasements 36 to sufficiently protect theribbon stacks 32 so that filler materials are not required.

The outer jacket 112 a can incorporate more than two outer strengthmembers 114 a. In addition, the outer jacket 112 a can be constructed ofa metallic material or a dialectric material. Also, the fiber opticcable 108 a can further include metal armor that extends around andfurther protects the optical module(s) 30.

Ninth Embodiment

FIG. 17 is a schematic end elevation view of a fiber optic cable 108 bin accordance with a ninth embodiment of the present invention. Thefiber optic cable 108 b of the ninth embodiment is identical to thefiber optic cable 108 a (FIG. 16) of the eighth embodiment, except fornoted variations and variations apparent to those of ordinary skill inthe art.

The fiber optic cable 108 b of the ninth embodiment includes multipleribbon stacks 32 (for example see FIG. 4) that are in a symmetricalstacked arrangement that is generally uniform along the length of thefiber optic cable and results in dense packaging of optical fibers. Themultiple ribbon stacks 32 are preferably components of multiple opticalmodules 30. The optical modules 30 are preferably not twisted, arepreferably generally polygonal, and are preferably maintained in thestacked symmetrical arrangement along the entire length of the fiberoptic cable 108 b. Although not shown in FIG. 17, the group of opticalmodules 30 can be collectively encircled by water-blocking tape (forexample, see the water-blocking tape 110 (FIG. 16)). Because the opticalmodules 30 are discreet units, operative optical modules can be readilysalvaged from the fiber optic cable 108 b if the fiber optic cablebecomes damaged.

Tenth Embodiment

FIG. 18 is a schematic end elevation view of a fiber optic cable 108 cin accordance with a tenth embodiment of the present invention. Thefiber optic cable 108 c of the tenth embodiment is identical to thefiber optic cable 108 b (FIG. 17) of the ninth embodiment, except fornoted variations and variations apparent to one of ordinary skill in theart.

The fiber optic cable 108 c of the tenth embodiment includes multipleribbon stacks 32 (for example see FIG. 4) that are stacked, but they arenot in a completely symmetrical arrangement. The multiple ribbons stacks32 are preferably components of multiple optical modules 30. The opticalmodules 30 are preferably not twisted and are preferably generallypolygonal and maintained in the stacked arrangement along the entirelength of the fiber optic cable 108 c.

Eleventh Embodiment

FIG. 19 is a schematic end elevation view of a fiber optic cable 108 din accordance with an eleventh embodiment of the present invention. Thefiber optic cable 108 d of the eleventh embodiment is identical to thefiber optic cable 108 a (FIG. 16) of the eighth embodiment, except fornoted variations and variations apparent to those of ordinary skill inthe art.

The fiber optic cable 108 c includes multiple ribbon stacks 32 (forexample see FIG. 4) that are laterally spaced apart from one another ina somewhat random arrangement so the optical modules are not in asymmetrical stacked configuration. The multiple ribbons stacks 32 arepreferably components of multiple optical modules 30. Whereas the fiberoptic cable 108 d of the eleventh embodiment is illustrated as includinga central strength member 116 in addition to the outer strength members114 a, it is preferred for the fiber optical cable 108 d to have eitherthe central strength member or the outer strength members, but not both.Although not shown, the group of optical modules 30 can be collectivelyencircled by water-blocking tape (for example, see the water-blockingtape 110 (FIG. 16)).

Twelfth Embodiment

FIG. 20 is a schematic end elevation view of a fiber optic cable 108 ein accordance with a twelfth embodiment of the present invention. Thefiber optic cable 108 e of the twelfth embodiment is identical to thefiber optic cable 108 d (FIG. 19) of the eleventh embodiment, except fornoted variations and variations apparent to those of ordinary skill inthe art.

In accordance with the twelfth embodiment, the multiple ribbon stacks 32(for example see FIG. 4) are tightly packed into the outer jacket 112 e.The multiple ribbons stacks 32 are preferably components of multipleoptical modules 30. As one example, the optical modules 30 can becharacterized as being in a somewhat random arrangement such that theyare not in a symmetrical stacked configuration. In accordance with thetwelfth embodiment, the enclosing of the optical modules 30 in thelongitudinally extending passage defined by the outer jacket 112 ecauses lateral forces to be applied to the at least one or more of theoptical modules so that those optical modules are transitioned fromtheir non-skewed configuration to their skewed configuration. Asdiscussed above and illustrated in FIG. 5, the skewed configurationoccurs when a buffer encasement 36 is laterally deformed and the opticalfiber ribbons 34 therein slide laterally relative to one another.

It is within the scope of the present invention for the enclosing of theoptical modules in the longitudinally passage defined by the outerjacket 112 e to include operations prior thereto. For example, thelateral forces that result in the skewed configuration of opticalmodules 30 can be caused when the optical modules are drawn together inpreparation for being enclosed in the outer jacket 112 e. As anadditional example, in accordance with the twelfth embodiment, the groupof optical modules 30 can be collectively encircled by water-blockingtape (for example, see the water-blocking tape 110 (FIG. 16)), and theapplication of the tape may result the lateral forces that result in theskewed configurations of at least some of the optical modules.

Thirteenth Embodiment

FIG. 21 is a schematic end elevation view of a fiber optic cable 118 ain accordance with a thirteenth embodiment of the present invention. Thefiber optic cable 118 a includes multiple ribbon stacks 32 (for examplesee FIG. 4), which are preferably components of optical modules 30. Morespecifically, the fiber optic cable 118 a includes a longitudinallyextending central member 120 a defining a longitudinally interiorpassage through which an optical module 30 longitudinally extends. Thecentral member can be a relatively strong central strength member, or itcan be a central spacer that is not as strong as the central strengthmember. The optical module 30 extending through the central member 120 acan be characterized as a central optical module. Multiple opticalmodules 30 are arranged radially around the periphery of the centralmember 120 a. Those radially arranged optical modules 30 can becharacterized as peripheral optical modules.

In accordance with the thirteenth embodiment, the ribbon stack 32 (seeFIG. 4 for example) of the central optical module 30 is in the form of astack of twelve optical fiber ribbons 34 (see FIG. 3 for example) witheach of those optical fiber ribbons containing twelve optical fibers 38(see FIG. 3 for example). In accordance with the thirteenth embodiment,each of the peripheral optical modules 30 is in the form of a stack oftwelve optical fiber ribbons 34 with each of those optical fiber ribbonscontaining twelve optical fibers 38. Therefore, the optical fiber cable118 a has a total fiber count of 1008. Variations of the optical fibercable 118 a have different fiber counts.

In accordance with the thirteenth embodiment, each of the opticalmodules 30 have approximately the same height H (FIG. 2) and each of theoptical modules have approximately the same width W (FIG. 2). In the endelevation view of the fiber optic cable 118 a, for each of theperipheral optical modules 30 the height H is the radial cross-dimensionof the peripheral optical modules, with the radial directions extendingfrom the center of the center optical module 30 toward the peripheraloptical modules.

Longitudinally extending strength members 122 extend between theperipheral optical modules 30, and a longitudinally layer of armor 124 aencircles the peripheral optical modules. A longitudinally extendingouter jacket 126 a constructed of a polymeric material extends aroundthe armor 124 a. In accordance with the thirteenth embodiment, thecentral optical module 30 is approximately centrally located withrespect to the outer jacket 126 a, and a radial distance is definedbetween the center of the central optical module and the center of eachof the peripheral optical modules 30. The radial distances definedbetween the center of the central optical module 30 and the center ofeach of the peripheral optical modules 30 are approximately equal.

In accordance with one version of the thirteenth embodiment, voidswithin the fiber optic cable 118 a are filled with a conventionalflooding material, such as a thixotropic gel. In contrast, in accordancewith another version of the thirteenth embodiment, interior spaces ofthe fiber optic cable 118 a are not filled with a flooding material,such as a thixotropic gel.

In accordance with a first version of the thirteenth embodiment, theperipheral optical modules 30 are not stranded. In accordance with thisfirst version, it is preferred for the central member 120 a not todefine a lay length. For example, FIG. 22 is an isolated perspectiveview of the central member 120 a of the fiber optic cable 118 a (FIG.21) in accordance with the first version of the thirteenth embodiment.As illustrated in FIG. 22, the outer surface of the central member 120 adoes not define a lay length.

In accordance with a second version of the thirteenth embodiment, theperipheral optical modules 30 are longitudinally stranded around thecentral member 120 a. In accordance with one example, the peripheraloptical modules 30 are helically stranded around the central member 120a, and in accordance with another example the peripheral optical modulesare S-Z stranded around the central member. In accordance with thissecond version, it is preferred for portions of the exterior surface ofthe central member 120 a to define the same type of stranding and laylength as the peripheral optical modules. For example, FIG. 23 is anisolated perspective view of the of the central member 120 a of thefiber optic cable 118 a (FIG. 21) in accordance with the second versionof the thirteenth embodiment.

As best seen in FIG. 21, the outer surface of the central member 120 adefines a six-sided polygon-like shape, and the fiber optic cable 118 acontains a corresponding number of peripheral optical modules 30. Inaccordance with an alternative to the thirteenth embodiment, the outersurface of the central member 120 a defines a circular shape. Inaccordance with another alternative to the thirteenth embodiment, thefiber optic cable 118 a does not include the central member 120 a, inwhich case stranding of the peripheral optical modules 30 is withrespect to the central optical module 30.

Fourteenth Embodiment

FIG. 24 is a schematic end elevation view of a fiber optic cable 118 bin accordance with a fourteenth embodiment of the present invention. Thefiber optic cable 118 b of the fourteenth embodiment is identical to thefiber optic cable 118 a (FIG. 21) of the thirteenth embodiment, exceptfor noted variations and variations apparent to those of ordinary skillin the art.

In accordance with the fourteenth embodiment, each of the opticalmodules 30 of the fiber optic cable 118b have approximately the samewidth W (FIG. 2), and the height H (FIG. 2) of the central opticalmodule 30 is greater than the height H of the peripheral optical modules30. Incorporating optical modules 30 having different heights H and/orwidths W advantageously provides for flexibility in cable designs andefficient packaging of optical fibers in fiber optic cables with highfiber counts.

In accordance with the fourteenth embodiment, the ribbon stack 32 (seeFIG. 4 for example) of the central optical module 30 is in the form of astack of eighteen optical fiber ribbons 34 (see FIG. 3 for example) witheach of those optical fiber ribbons containing twenty-four opticalfibers 38 (see FIG. 3 for example). In accordance with the fourteenthembodiment, each of the peripheral optical modules 30 is in the form ofa stack of six optical fiber ribbons 34 with each of those optical fiberribbons containing twenty-four optical fibers 38. Therefore, the opticalfiber cable 118 b has a total fiber count of 1296. Variations of theoptical fiber cable 118 b have different fiber counts.

Fifteenth Embodiment

FIG. 25 is a schematic end elevation view of a fiber optic cable 118 cin accordance with a fifteenth embodiment of the present invention. Thefiber optic cable 118 c of the fifteenth embodiment is identical to thefiber optic cable 118 a (FIG. 21) of the thirteenth embodiment, exceptfor noted variations and variations apparent to those of ordinary skillin the art.

In accordance with the fifteenth embodiment, both the height H (FIG. 2)and the width W (FIG. 2) of the central optical module 30 is greaterthan the height H and width W of each of the peripheral optical modules30. In accordance with the fifteenth embodiment, the ribbon stack 32(see FIG. 4 for example) of the central optical modules 30 is in theform of a stack of eighteen optical fiber ribbons 34 (see FIG. 3 forexample) with each of those optical fiber ribbons containing twenty-fouroptical fibers 38 (see FIG. 3 for example). In accordance with thefifteenth embodiment, each of the peripheral optical modules 30 is inthe form of a stack of twelve optical fiber ribbons 34 with each ofthose optical fiber ribbons containing twelve optical fibers 38.Therefore, the optical fiber cable 118 c has a total fiber count of1296. Variations of the optical fiber cable 118 c have different fibercounts.

Sixteenth Embodiment

FIG. 26 is a schematic end elevation view of a fiber optic cable 118 din accordance with a sixteenth embodiment of the present invention. Thefiber optic cable 118 d of the sixteenth embodiment is identical to thefiber optic cable 118 c (FIG. 25) of the fifteenth embodiment, exceptfor noted variations and variations apparent to those of ordinary skillin the art. In accordance with the sixteenth embodiment, the outersurface of the central member 120 d defines an eight-sided polygon-likeshape and there are eight peripheral optical modules. Therefore, theoptical fiber cable 118 d has a total fiber count of 1584.

The fiber optic cables 118 a-c (FIGS. 21 and 24-26) illustrate that infiber optic cables of this type, maximum packaging efficiency may beachieved with a central stack of optical fiber ribbons with relativelywide (relatively high fiber count) ribbons and peripheral stacks ofoptical fiber ribbons with relatively narrow (relatively low fibercount) ribbons.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A fiber optic cable, comprising: a stack ofoptical fiber ribbons extending in a longitudinal direction, whereineach optical fiber ribbon comprises a laterally extending array oflongitudinally extending optical fibers that are bonded together as aunit; and a longitudinally extending buffer encasement comprising: alongitudinally extending inner portion having a modulus of elasticityand comprising an interior surface, wherein the interior surface extendsaround and defines a longitudinally extending passage that contains thestack, with the interior surface closely bounding the stack, and alongitudinally extending outer portion extending around, closelybounding and contacting the inner portion, and having a modulus ofelasticity that is greater than the modulus of elasticity of the innerportion.
 2. A fiber optic cable according to claim 1, wherein theinterior surface of the inner portion engages a substantial portion ofthe periphery of the stack.
 3. A fiber optic cable according to claim 1,wherein the interior surface of the buffer encasement is unadhered tothe stack and the stack is capable of moving relative to the bufferencasement.
 4. A fiber optic cable according to claim 1, wherein theperiphery of the stack defines a shape in an end elevation view of thestack, and the interior surface of the inner portion of the bufferencasement defines a shape in an end elevation view of the bufferencasement that is substantially similar to the shape defined by theperiphery of the stack in the end elevation view of the stack.
 5. Afiber optic cable according to claim 4, wherein in the end elevationview of the buffer encasement, the exterior surface of the bufferencasement defines a shape that is substantially similar to the shapedefined by the periphery of the stack in the end elevation view of thestack.
 6. A fiber optic cable according to claim 1, further comprising alongitudinally extending jacket defining a longitudinally extendingjacket passage, wherein the buffer encasement extends within the jacketpassage.
 7. A fiber optic cable according to claim 1, wherein: the innerportion further comprises an exterior surface that extends around and isspaced apart from the passage; and the outer portion comprises aninterior surface that extends around, closely bounds, and engages theexterior surface of the inner portion, whereby the buffer encasement hasa plurality of plies.
 8. A fiber optic cable according to claim 7,wherein the buffer encasement is sufficiently rigid to maintain thestack in a stacked configuration and sufficiently flexible to allow theoptical fiber ribbons to slide laterally relative to one another sothat, in an end elevation view of the stack, the stack and the bufferencasement can transition from a non-skewed configuration to a skewedconfiguration, wherein the lateral displacement between the opticalfiber ribbons in the skewed configuration is different from the lateraldisplacement between the optical fiber ribbons in the non-skewedconfiguration.
 9. A fiber optic cable according to claim 7, wherein thestack is longitudinally twisted, the buffer encasement is sufficientlyrigid to hold the stack in the longitudinally twisted configuration, andthe buffer encasement is thin such that an exterior surface of the outerportion of the buffer encasement defines ridges that correspond to thetwist of the stack.
 10. A fiber optic cable according to claim 7,wherein: each optical fiber ribbon comprises a pair of longitudinallyextending opposite edges and a pair of longitudinally extending oppositesurfaces that extend laterally between the edges, and each optical fiberribbon has a thickness defined between its opposite surfaces; and thebuffer encasement is a relatively thin, and in an end elevation view ofthe buffer encasement at least a majority of the buffer encasement has athickness defined between the interior surface of the inner portion ofthe buffer encasement and an exterior surface of the outer portion ofthe buffer encasement, and the thickness of the buffer encasement is notsubstantially greater than the thickness of each of the optical fiberribbons.
 11. A fiber optic cable according to claim 1, wherein a surfaceis not defined between the inner portion and the outer portion.
 12. Afiber optic cable according to claim 11, wherein the buffer encasementis sufficiently rigid to maintain the stack in a stacked configurationand sufficiently flexible to allow the optical fiber ribbons to slidelaterally relative to one another so that, in an end elevation view ofthe stack, the stack and the buffer encasement can transition from anon-skewed configuration to a skewed configuration, wherein the lateraldisplacement between the optical fiber ribbons in the skewedconfiguration is different from the lateral displacement between theoptical fiber ribbons in the non-skewed configuration.
 13. A fiber opticcable according to claim 11, wherein: each optical fiber ribboncomprises a pair of longitudinally extending opposite edges and a pairof longitudinally extending opposite surfaces that extend laterallybetween the edges, and each optical fiber ribbon has a thickness definedbetween its opposite surfaces; and the buffer encasement is a relativelythin, and in an end elevation view of the buffer encasement at least amajority of the buffer encasement has a thickness defined between theinterior surface of the inner portion of the buffer encasement and anexterior surface of the outer portion of the buffer encasement, and thethickness of the buffer encasement is not substantial greater than thethickness of each of the optical fiber ribbons.
 14. A fiber optic cableaccording to claim 11, wherein the stack is longitudinally twisted, thebuffer encasement is sufficiently rigid to hold the stack in thelongitudinally twisted configuration, and the buffer encasement is thinsuch that an exterior surface of the outer portion of the bufferencasement defines ridges that correspond to the twist of the stack. 15.A fiber optic cable according to claim 1, wherein the stack is in alongitudinally twisted configuration and the buffer encasement isoperative to hold the stack in the longitudinally twisted configuration.16. A method of manufacturing a fiber optic cable, comprising the stepsof: advancing in a longitudinal direction a longitudinally extendingstack of optical fiber ribbons; and encasing the stack in an singlelongitudinally extending buffer encasement having: a longitudinallyextending inner portion having a modulus of elasticity and comprising aninterior surface, wherein the interior surface extends around anddefines a longitudinally extending passage that contains the stack, withthe interior surface closely bounding and engaging a substantial portionof the periphery of the stack, and a longitudinally extending outerportion extending around and closely bounding the inner portion, andhaving a modulus of elasticity that is greater than the modulus ofelasticity of the inner portion.
 17. A method of manufacturing a fiberoptic cable according to claim 16, further comprising the step oflubricating exterior surfaces of the optical fiber ribbons prior to thestep of encasing the stack.
 18. A method of manufacturing a fiber opticcable according to claim 16, further comprising the step of encasing thebuffer encasement in a longitudinally extending jacket.
 19. A method ofmanufacturing a fiber optic cable according to claim 16, wherein thestep of encasing comprises the steps of coating the stack with anultraviolet-curable material and thereafter exposing theultraviolet-curable material to ultraviolet radiation for apredetermined period of time selected so that on a per unit basis morecuring occurs in the outer portion than the inner portion.
 20. A methodof manufacturing a fiber optic cable according to claim 16, wherein thestep of encasing comprises the steps of extruding a first extrusionaround the stack and extruding a second extrusion around the firstextrusion so that the interior surface of the second extrusion comesinto contact with the exterior surface of the first extrusion prior tosolidification so that the interior and exterior surfaces become blendedtogether.
 21. A method of manufacturing a fiber optic cable according toclaim 16, wherein the step of encasing comprises the steps of applying afilm around the stack and extruding an extrusion around the film,wherein the step of applying the film is selected from the stepsconsisting of longitudinally folding and helically wrapping the filmaround the stack.
 22. A method of manufacturing a fiber optic cableaccording to claim 16, wherein the step of encasing comprises the stepsof extruding an extrusion around the stack and applying a film aroundthe extrusion, wherein the step of applying the film is selected fromthe steps consisting of longitudinally folding and helically wrappingthe film around the stack.
 23. A method of manufacturing a fiber opticcable according to claim 16, wherein the step of encasing comprises thesteps of applying a first film around the stack and applying a secondfilm around the first film, wherein the step of applying the first filmis selected from the steps consisting of longitudinally folding andhelically wrapping the first film around the stack, and the step ofapplying the second film is selected from the steps consisting oflongitudinally folding and helically wrapping the second film around thestack.